docs: def get_radius_normal(lat_radians: float, ell: Ellipsoid = None) -> float:
      """
      Compute normal radius of planetary body
  
      Parameters
      ----------
  
      lat_radians : float
          latitude in radians
      ell : Ellipsoid, optional
          reference ellipsoid
  
      Returns
      -------
  
      radius : float
          normal radius (meters)
      """
      if ell is None:
          ell = Ellipsoid()
  
      a = ell.a
      b = ell.b
  
      return a**2 / sqrt(a**2 * cos(lat_radians)**2 + b**2 * sin(lat_radians)**2)